Hospital-Acquired Infections: Risk Factors, Causes, and Treatment

Posted on May 6, 2024 in Medicine & Health

Factors Predisposing to Hospital Infection

Hospital-acquired infections (HAIs) appear within 3 days after a patient is admitted.

Routes of Transmission

• Contact
• Droplets
• Airborne
• Vehicle
• Vector

Hospitalized Patients at High Risk for Infection

Hospitalized patients are at a higher risk for infection due to:

• Underlying illness
• Environment
• Microbiological/virulence factors
• Procedures and interventions
• Process of care

IV. Extrinsic Factors

• Medical treatment and interventions (e.g., invasive devices)
• Chemotherapy (immunosuppression and mucous disruption)
• Nasogastric feeding tubes
• Surgical operations
• Antibiotic use

Characteristics of Hospital Microorganisms: The Problem with Antibiotic Resistance

• Any organism can cause HAIs.
• Antibiotic use has changed the mode of distribution.

With more potent and broad-spectrum antibiotics and improved medical techniques:

1. Increased incidence of antibiotic-resistant gram-positive bacteria
2. Emergence of antibiotic-resistant gram-negative organisms that produce beta-lactamase

These organisms are highly aggressive, virulent, and resistant.

• Many organisms are considered “opportunistic” and are unable to cause disease in healthy people with good immune systems.
• E. coli is the most common nosocomial infection.

General Markers of Determination

1. High resistance (to 2-3 antibiotics)
2. Susceptibility to bacteriophage test
3. Genetic test (map comparison)

Hospital-Acquired Pneumonia (HAP)

Pneumonia Classification

1. CAP (community-acquired pneumonia)
2. HCAP (healthcare-associated pneumonia)
   1. HAP or NP (hospital or nosocomial pneumonia)
   2. VAP (ventilator-associated pneumonia): Develops 48-72 hours after endotracheal intubation

HAP/NP is pneumonia that develops more than 48 hours after admission.

• Early: Up to 5 days
• Late: More than 5 days

Agents Causing HAP

HAP occurs in non-intubated patients, both inside and outside the ICU. It is similar to VAP but with a higher frequency of non-multidrug-resistant (MDR) pathogens.

Factors Contributing to HAP Contraction

1. Increased age
2. Decreased filtration of inspired air
3. Intrinsic respiratory, neurologic, or other diseases
4. Trauma (abdominal) surgery
5. Medications
6. Decreased lung volumes/decreased clearance of secretions
7. Poor hand-washing and inadequate disinfection
8. Respiratory devices causing cross-contamination

Empirical Treatment for HAP

• Treatment must be started once a diagnostic specimen is obtained.
• Factors for selecting agents in the presence of risk factors for MDR pathogens.
• Most patients without risk factors for MDR pathogens can be treated with a single agent.
• Standard recommendation with risk factors for MDR infection is 3 antibiotics: 2 against P. aeruginosa and 1 against MRSA.

Specific Treatment for HAP

• Once an etiological diagnosis is made, broad-spectrum empirical treatment can be modified to target the known bacteria.

Hospital-Acquired Urinary Tract Infection (UTI)

Nosocomial UTIs are the most common nosocomial infections, occurring in both acute and long-term care settings.

Risk Factors for Hospital-Acquired UTI

• Devices (5-10%): Indwelling catheters
• Increased hospital stay
• Female gender
• Lack of systemic antibiotic treatment
• Microbe colonization of drainage bag
• Catheter care violations
• Metal colonization
• Old age
• Diabetes mellitus
• Absence of drip chamber

Causes of UTI

1. Direct inoculation of microorganisms into the bladder
2. Catheter damage to the GAG layer of the bladder
3. Residual urine from the bladder that doesn’t drain

Agents Causing UTI

Aerobic gram-negative rods, particularly E. coli, are the most common cause of UTIs, often acquired from endogenous colonic flora.

Rational Choice of Antibiotic Treatment for UTI

• Choice of antibiotic agent for empiric treatment should be based on:
  1. Urine Gram stain type
  2. Previous urine culture results
  3. Risk of multidrug resistance (greater in patients with nosocomial UTI)
• Mild to moderate cases: Urinary fluoroquinolones (ciprofloxacin, levofloxacin) or broad-spectrum cephalosporins
• Potential concerns due to:
  1. Increase in fluoroquinolone resistance
  2. Frequency of Enterococcus infections
• Patients with evidence of pyelonephritis/urosepsis: Broad-spectrum antibiotics (piperacillin-tazobactam or carbapenems)
• Presence of cocci (Enterococcus or Staphylococcus) in urine: Vancomycin
• Treatment duration: 7-10 days, 7-14 days, or 7-21 days depending on severity and causative agent

Catheter-Related Bacteremia

Risk Factors for Device-Related Bacteremia

• Granulocytopenia
• Immunosuppressive therapy
• Loss of skin integrity
• Severe underlying disease
• Not washing hands (healthcare providers)
• Alteration of cutaneous microflora
• Catheter composition (flexibility/stiffness, thrombogenicity, size, number of lumens, duration of placement >72 hours, type of catheter balloon tip, flow)

Agents Causing Bacteremia

• Coagulase-negative staphylococci are the most common pathogens causing bacteremia (31%)
• S. aureus causes 16% of cases
• Candida (8%)
• Klebsiella pneumoniae (5%)
• Enterobacteriaceae spp. (4%)

The most common nosocomial fungal cause of bloodstream infection is Candida, with a mortality rate of 40-60%.

Microbiology of Device-Associated Bacteremia

• Coagulase-negative staphylococci
• Staphylococcus aureus
• Enterococcus
• Serratia
• Candida albicans
• Pseudomonas aeruginosa
• Klebsiella
• Enterobacteriaceae